A downhole perforating gun switch is located in the sub housing and has first, second and intermediate contacts, with the intermediate contact located between the first and second contacts. In an initial position, the intermediate and second contacts are in contact with each other, while the intermediate and first contacts are out of contact with each other. A thermoplastic plug is positioned between the intermediate and second contacts. A conductive sleeve or enclosure provides the electrical contact between the intermediate and second contacts. When the switch is subjected to detonation effects from the perforating gun, the second contact, the plug, and the intermediate contact are moved toward the first contact, wherein the first and intermediate contacts contact each other and the intermediate and second contacts are out of contact with each other.